The present invention relates to a sputtering apparatus and, more particularly, to a magnetron type sputtering apparatus which is adapted to prevent inferior sputtering attributable to bumping or sudden boiling.
In order to enhance the performance of semi-conductor devices, P-N junctions of the semiconductor devices have become shallower and patterns have become finer. Additionally, it has become necessary to adopt aluminum alloy materials such as, for example, Al-Si and Al-Si-Cu, and high melting metal materials such as, for example, Mo, W, and Pt as electrode wiring materials. However, such materials are difficult to treat with conventional vacuum evaporators.
Previously, sputtering apparatus have been principally utilized for thin-film ICs and such apparatus are difficult to apply to the formation of electrodes of semiconductor devices since, for example, the deposition rate is relatively low and there is a rise in the substrate temperature resulting in a damaging of the semiconductor device.
However, in an attempt to solve the above-noted problems, in recent years, a magnetron type sputtering apparatus has been developed which utilizes an orthogonal electromagnetic el field. Magnetron type sputtering apparatus have been put into practical use in electrode wiring steps of semiconductor devices.
A magnetron type sputtering apparatus may be classified into various types depending upon the arrangements of the magnets and the shapes of the targets. However, any magnetron type sputtering apparatus is based upon the principal that a plasma moving in conformity with the Lorentz equation is confined into a local space in a vicinity of a target by utilizing an orthogonal electromagnetic field. More particularly, electrons execute a cycloid motion on the target and collide against gas molecules resulting in a generation of plasma of a high density. Since the electrons are constrained by the magnetic field, it is possible to prevent a temperature increase and damage to the semiconductor device due to the bombardment of the wafer with electrons.
Generally, a magnetron type sputtering apparatus is constructed so that, in a vicinity of a target or cathode, disposed in opposition to an
anode, magnets (permanent magnets or electromagnets) are disposed to form the electromagnetic field near the target, with the plasma being confined on the target by utilizing the cycloid motion of the electrons in order to obtain a high sputtering rate.
An extensively used sputtering apparatus known as a "Sputter System 3125H", manufactured by Varian, Inc, is based on the principle that argon gas, introduced in a vacuum chamber of the apparatus, is ionized and a target or film material is struck by the ions. A ring magnetron or a S-GUN, is employed for ionizing the argon and accelerating the ions, with the S-GUN forming a plasma discharge having a doughnut-shape. The plasma discharge is established by an electric field and a magnetic field, and the argon molecules are ionized and the target is bombarded with the ions by the plasma discharge. Since the plasma is formed in a doughnut shape just on the target, most of the secondary electrons are confined within the plasma.
In the above-noted system, the S-GUN is incorporated into a chamber with the system also including a planetary type substrate jig and a rotating mechanism, along with a liquid nitrogen cold trap, a diffusion pump, an ion gauge, a main valve, a variable orifice for regulating the argon gas, and a substrate heater.
In use, a substrate is set on a member of the planetary type substrate jig and, for example, up to three members may be put in the chamber. The chamber is then closed or sealed by a door and a preliminary evacuation is begun, with the evacuation being effected by a mechanical pump. Subsequently, the diffusion pump is actuated to begin a main evacuation of the chamber. The members of the planetary type substrate jig revolve around the S-GUN while revolving around their own axes and, when a degree of vacuum of the order to 10.sup.-6 Torr has been reached, the heater in the chamber may be turned "on" to attain a set temperature. After a thermal equilibrium has been reached, a RF etching is performed; however, the heating and etching processes are optional. Thereafter, the argon gas is introduced, and the argon gas is maintained in the chamber at a pressure of up to the order to 10.sup.-3 Torr, whereupon the sputtering begins.
In the above noted system, since a distance from the S-GUN to the substrate is about 50 cm, the influence of the secondary electrons is substantially avoided and a favorable uniformity and step coverage are attained by a good angle of incidence at which the target molecules are deposited on the substrate. Furthermore, the jig of the substrates revolves on its own axis and also around the S-GUN so as to further improve the uniformity and step coverage. When the deposition on the substrate has ended, dry nitrogen is introduced to restore the interior of the chamber to atmospheric pressure thereby terminating one cycle of operation.